[jira] [Commented] (HBASE-4823) long running scans lose benefit of bloomfilters and timerange hints

["Prakash Khemani (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-4823?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13153655#comment-13153655 ] 

Prakash Khemani commented on HBASE-4823:
----------------------------------------

https://issues.apache.org/jira/browse/HBASE-3415 is also related
                
> long running scans lose benefit of bloomfilters and timerange hints
> -------------------------------------------------------------------
>
>                 Key: HBASE-4823
>                 URL: https://issues.apache.org/jira/browse/HBASE-4823
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Kannan Muthukkaruppan
>            Assignee: Kannan Muthukkaruppan
>
> When you have a long running scan due to say an MR job, you can lose the benefit of timerange hints & bloom filters midway if your scanner gets reset. [Note: The scanners can get reset say due to a flush or compaction].
> In one of our workloads, we periodically want to do rollups on recent 15 minutes of data in a column family... but the timerange hint benefit is lost midway when this resetScannerStack (shown below) happens. And end result-- we end up reading all the old HFiles rather than just the recent HFiles.
> {code}
>  private void resetScannerStack(KeyValue lastTopKey) throws IOException {
>     if (heap != null) {
>       throw new RuntimeException("StoreScanner.reseek run on an existing heap!");
>     }
>     /* When we have the scan object, should we not pass it to getScanners()
>      * to get a limited set of scanners? We did so in the constructor and we
>      * could have done it now by storing the scan object from the constructor */
>     List<KeyValueScanner> scanners = getScanners();
> {code}
> The comment in the code seems to be aware of this issue and even has the suggested fix!

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